Process for producing polysiloxane useful as brake fluids

ABSTRACT

A PROCESS FOR FORMING AN ESTER POLYSILOXANE COMPRISING REACTING IN THE PRESENCE OF WATER, A DIORGANOPOLYSILOXANE OF THE FORMULA R2SIX2 WITH CYCANOALKYLCHLOROSILANE OF THE FORMULA RSI(X)2GCN AND A SILANE OF THE FORMULA R&#39;&#39;R2SIX WHEREMR IS SELECTED FROM MONOVALENT HYDROCARBON RADICALS AND HALOGENATED MONOVALENT HYDROCARBON RADICALS R&#39;&#39; IS THE SAME AS R OR -CGH2GCN,X IS A HYDROLYZABLE RADICALS SELECTED FROM HALOGEN, ALKOXY, ARYLOXY AND ACYLOXY RADICALS,EG IS A WHOLE NUMBER THAT VARIES FROM 1 TO 20, TO OBTAIN A POLYSILOXANE, WHICH POLYSILOXANE IS THEN ESTERIFIED IN THE PRESENCE OF A CATALYST WITH AN ALCOHOL.

United States Patent 3,813,425 PROCESS FOR PRODUCING POLYSILOXANE USEFUL AS BRAKE FLUIDS Frank J. Traver, Troy, N.Y., assignor to General Electric Company No Drawing. Filed Mar. 17, 1971, Ser. No. 125,396

Int. Cl. C07f 7/08 US. Cl. 260448.2 E 11 Claims ABSTRACT on THE DISCLOSURE A process for formin an ester polysiloxane comprising reacting in the presence of water, a diorganopolysiloxane of the formula RzSiXz with eyanoalkylchlorosilane of the formula RSi(X) C H CN and a silane of the formula RR SiX where R is selected from monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, R- is the same as R or -C H CN, X is a hydrolyzable radical selected from halogen, alkoxy, aryloxy and acyloxy radicals, g is a whole number that varies from 1 to 20, to obtain a polysiloxane, which polysiloxane is then esterified in the presence of a catalyst with an alcohol.

BACKGROUND OF THE INVENTION This invention relates to a process for forming ester polysiloxanes and, in particular, this invention relates to a process for forming ester polysiloxanes useful as brake fluids by esterifying carboxyalkylpolysiloxanes.

It is desirable that a fluid which is to be used as a brake fluid meet certain performance criteria as well as certain suggested criteria for safety purposes, that is, the brake fluid must be such so that the brakes will operate efiiciently and failure of the brakes will not result. The suggested criteria which a brake fluid must meet encompass an original equilibrium reflux boiling point determination, a wet equilibrium reflux boiling point determination, flash point determination, kinematic viscosity determination, pH value, brake fluid stability which encompasses high temperature stability and chemical stability, a corrosion determination, evaporation determination, Water tolerance determination at low temperatures and at 60 C., compatibility determination at low temperatures, a resistance to oxidation determination, elfects on rubber determination and stroking property determination. The original equilibrium reflux boiling point determination is desired in order to determine that the brake fluid have a sufliciently high boiling temperature so that it will not boil at operating temperatures to which the brake fluid is subjected through the normal operation of the vehicle. It can easily be seen that if the equilibrium reflux boiling point is too low, that the vaporized brake fluid would easily rupture the brake hoses, resulting in failure of the brakes. Further, the brakes would not operate with vapor in the hydraulic lines.

A wet equilibrium boiling point is desired so as to test whether the inclusion of a certain amount of water in the brake fluid would result in the formation of vapor in the normal operating temperatures of the brake fluid, which would cause the rupture of the brake lines and result in failure of the brakes.

A flash point test is necessary to determine whether the brake fluid has a sufficiently high flash point. If the brake fluid does not have a sufliciently high flash point, it will start burning at the normal operating temperatures of the brakes. It is also desirable in this respect to test the fire point and the autogenous ignition temperature. For instance, if the fire point is close enough to the flash point under normal operating conditions when the flash point of the brake fluid is exceeded, the brake fluid might continue burning and would thus not only result in failure of 3,813,425 Patented May 28, 1974 ice the brakes but cause the automobile to burst into flames. In accordance with this reasoning, it is also desirable to consider the autogenous ignition temperature, for if this temperature is not considerably higher than the flash point, it can be seen that again, under operating conditions when the flash point of the fluid is exceeded and in that case if the autogenous ignition temperature of the fluid is also exceeded, the brake fluid might burn so quickly that not only will the brakes fail but the occupant of the automobile will not have time to leave the automobile before a major fire ensues.

A kinematic viscosity test is necessary to determine whether the brake fluid will have sufliciently low viscosity at very low temperatures and a sufficiently minimum viscosity at high temperatures so that the brakes will be in acceptable operating condition at these extreme temperatures.

A pH test is used to determine the pH of the brake fluid such that it is not acidic or too basic so that it will corrode and eat away the hydraulic lines or the hydraulic brake drum cylinders in which the fluid is located.

A high temperature stability test is necessary to determine the stability of a fluid at high temperatures so that it will not degrade at the specified temperatures to other compounds or products which would be unworkable fluids for a brake system.

A chemical stability test is needed to determine whether if the brake fluid is mixed with a glycol brand brake fluid it will not react with this fluid.

A corrosion test, as with the pH test, is needed to determine whether the brake fluid would eat away the metal in the hydraulic lines or the rubber in the brake drum cylinders or the rubber that may form part of the hydraulic lines and thus cause early failure of the brakes.

An evaporation test is needed to determine whether the brake fluid will evaporate at certain high temperatures and thus not only form undesirable vapor in the brake lines but further will result in the dissipation of the brake fluid through the hydraulic lines and master cylinder into the atmosphere so that it would need constant replacement. Excessive vapor in the hydraulic lines would cause brake failure.

A water tolerance test at low temperatures is needed to determine whether the fluid with the Water it would pick up from the atmosphere would result in the water crystallizing out to form ice at low temperatures, which ice would impair the performance of the brakes.

A water tolerance test at high temperatures is needed to determine whether the Water which is picked up by the fluid from the atmosphere would evaporate at the high temperature and form vapor in the brake lines which would impair the performance of the brakes.

A compatibility test is needed to determine at both low and high temperatures whether the brake fluid would operate properly when it is mixed with glycol based brake fluid and result in impairment of the performance of the brakes. This test is needed because it frequently becomes necessary to replace part of the brake fluid in an automobile with additional fluid so it is desirable for any new brake fluid which is admitted to the market to be compatible with glycol based brake fluids.

A resistance to oxidation test is necessary in order to determine whether the brake fluid will oxidize in the presence of the oxygen in the air to form different products which would be unsuitable as brake fluid components.

A stroking properties test is necessary in order that the fluid can he tested in a simulated operation that would be comparable to the use of the fluid in an automobile and thus determine the performance of the brake fluid over an extended period of time so that it may be determined that the brake fluid tested does not have any unforeseen effects which will degrade the brake hydraulic system in failure of'the brakes.

At the present time, thereare no brake fluids presently on the market which pass all of the above tests with acceptable overall performance. The desirable specifications or ratings in the above suggested tests require the fluid to have a higher equilibrium reflux boiling temperature and flash point than of the presently available glycol based fluids.

The brake fluid presently on the market are basically polyether glycols which vary from case to case, depending on the type of polyether units and the number of polyether units in the polymer chain. Such brake fluids are hygroscopic in that they will pick up large quantities of water from the atmosphere. Problems are associated with the packaging and handling of such brake fluids since unless extreme precautions are exercised these brake fluids will pick-up large amounts of water from the atmosphere due to their hygroscopicity which will result in a brake fluid with poor performance characteristics as well as a brake fluid that is unsafe because it can cause a failure of the brakes. It is undesirable to have excess water since it will separate out at low temperatures such as 40 F. in that the water will form ice crystals and may cause the brake drum cylinder to freeze, thus causing failure of the brakes. Further, it is undesirable to have large amounts of water in the brake fluid in that at the high temperatures, which are commonly present in the operation of automobile brakes, the water will evaporate to form vapor which may rupture the hydraulic lines causing failure of the brakes and possibly cause the brake fluid to burst into flames or the vapor may cause a very sluggish, ineflicient braking action.

It is thus desirable to have a brake fluid on the market which picks up a minimum amount of water through hygroscopicity and which is compatible with the amount of water it picks up from the atmosphere so that when the brake fluid is subjected to temperatures as low as -40 F., brake failure does not result. The 'brake fluids which meet the above tests are disclosed in the present case as well as in the applications of Frank I. Travers Ser. No. 125,398, Frank J. Travers Ser. No. 125,397, and Frank J. Traver's Ser. No. 132,556, now US. Pat. No, 3,725,287, all filed on the same date.

The process of the present invention produces ester polysiloxanes which have been found to be very useful as brake fluids. These compounds are claimed in the copending application of Frank I. Travers, entitled Polysiloxanes Useful as Brake Fluids Ser. No. 125,398 filed on the same day as the present case. In this copending case, there is disclosed a process by which the ester polysiloxanes are obtained by esterifying an alkenoic acid with an alcohol and then taking the resulting alkenoic acid ester and reacting it with a hydropolysiloxane in the presence of a platinum catalyst so that the alkenoic acid ester is added onto the hydrogens located in the hydropolysiloxane by an SiH-olefin addition reaction.

The present case presents an alternative process for forming the same type of compounds. However, the present process takes the steps of first forming a carboxyalkylpolysiloxane and then esterifying the acid groups on the polysiloxane with alcohols to produce the resulting ester polysiloxane. The ester polysiloxanes formed by the present invention have all the advantageous properties and meet all of the specifications set forth above in the discussion of brake fluids.

Although the copending application, as well as the process of the. present case provide for ester polysiloxanes of the same structure which have many advantages as brake fluids, the present process does notv necessitate the use of a platinum catalyst which platinum catalyst is expensive and can be easily contaminated. Accordingly, there is provided by the present process a very simple and direct means for forming the ester polysiloxanes where all of the starting materials are standard materials Well known in silicone or result chemistry. The process may be easily followed by those skilled in the art to obtain ester pblysiloxanes high yield. 1

It is one object of the present invention to provide an efiicient process for producing es'terpolysiloxanes. M

It is another object of the present invention to provide a process for producing polysiloxanes jhaving carboxy groups thereon, which carboxy groups may be esterified with an alcohol to produce the resulting ester.

It is still another object of the present invention to provide polysiloxanes having ester groups thereon by hydr-olyzing silanes including the nitrile silanes, and then esterifying the resulting condensed polysilox-ane product with an alcohol.

It is yet another aim of the present invention to provide polysiloxanes with estergroups thereon byequilibrating cyclic polysiloxanes and then esterifying the resultant polysiloxane having carboxy groups thereon with an alcohol. These and other objects of the invention are obtained by means of the invention set forth below.

SUMMARY OF THE INVENTION In accordance with the objects set forth .below, there is provided by the present invention a process for forming an ester polysiloxane useful as a brake fluid comprising reacting in the presence of water a diorganopolysiloxane of the formula 1 R SiX with a cyanoallcylchlorosilane of the formula, (2) RSi(X )C H CN and a silane of the formula,

(3) RR SiX where R is selected from monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals. R is the same as R or C, H CN, X is a hydrolyzable radical selected from halogen, alkoxy aryloxy and acyloxy radicals, g is a whole number that varies from 1 to 20, to obtain a polysiloxane of the formula, I

(4) R'Risi0(Rsio ,(Rzsi0).SiRzR .u ooon and then esterifying the above product in the presence of a catalyst with an alcohol selected from the group con: sisting R OH, R OR OH,

R ii-OR0E, R -R OH, HOR OH, and HOR (()H) where y varies from 1 to 10, z varies from 1 to 15, R is selected from mono; valent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, R is a polyvalent hydrocarbon ra d ical with s plus 1 hydroxyl groups attached. thereto, s is a whole number that varies from 1 to 5, and R is a divalent hydrocarbon radical selected from alkylene and arylene radicals of up to 20 carbon atoms,to produce'a polysiloxanes of the formulas,

(5) nooomi mz)stoutsi0 RtsiO).sinsomi ooon ,m ooo s V rnflooon where E is selected from R*, R 0R HOR OH and HOR (OH) where the above symbols have the meanings defined previously. 1

The desired polysiloxane of formulas (5) and (6) may also be prepared by taking the silanes of'formula (1)and formula (2) separately and condensingthem' in the presence of a strong base or acid to form the corresponding cyclopolysiloxanes. The corresponding cyclopolysiloxanes DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The radicals R and R as well a R appearing in the above formulas are well known in the art and typified by radicals usually associated with silicon-bonded organic groups in the case of R, R and generally associated with divalent hydrocarbon radicals in the case of R The organic radicals represented by R and R include monovalent hydrocarbon radicals, halogenated monovalent hydrocarbon radicals and cyanoalkyl radicals. Thus, the radicals R and R may be alkyl, such as methyl, ethyl, propyl, butyl, octyl; aryl radicals, such as phenyl, tolyl, xylyl, naphthyl, radicals; aralkyl radicals, such as benzyl, phenylethyl radicals; olefinic unsaturated monovalent hydrocarbon radicals, such as vinyl, allyl, cyclohexyl radicals; cycloalkyl radicals, such as cyclohexyl, cycloheptyl radicals; halogenated monovalent hydrocarbon radicals such as chloromethyl, dichloropropyl, 1,1,1-trifluoropropyl, chlorophenyl, dibromophenyl and other such radicals; cyanoalkyls radicals, such as cyanoethyl, cyanopropyl, etc. Preferably the radicals represented by R and R have less than 8 carbon atoms and, in particular, it is preferred that R and R be methyl, ethyl or phenyl. The radicals represented by R are generally the same radicals as R or the radical C H CN. The radicals represented by R may be any alkylene or arylene radicals of up to 20 carbon atoms, such as methylene, ethylene, various isomers of phenylene radicals or substituted phenylene radicals. In the preferred embodiment, R is methyl. Further, R can be alkylene, arylene and alkynylene. In formula (3) and in other formulas where the radical C H C'N appears, g is preferably equal to 2 or 3 and may be equal to a value of as high as 20. Depending on whether R is equal to a radical which is the same as the R radical or the nitrile radical, there are two preferred types of compounds which may be obtained by the process of the present invention and which are represented in formulas (5) and (6).

Some of the preferred esterified products which come within formulas (5) and (6) are as follows:

The diorganosilanes of formula (1) are preferably ones in which X is equal to chlorine or equal to another type of halogen. However, it is to'be understood in the present invention that X may be also represented by an acetoxy, aryloxy or an acyloxy hydrolyzable radical. Such diorganosilanes are well known in the art. The silanes of formula (3) are also well known in the art. l

The cyanoalkylsilanes of formula (2) may be prepared by various methods which are known in the art and which will be set forth in detail below.

Illustrative of the diorganohalogensilanes within the scope of formula 1) are dimethyldichlorosilane, methylphenyldichlorosilane, diphenyldichlorosilane, ethylpropyldichlorosilane, etc. Products within the scope of formula 2) include for example, methyl-beta-cyanoethyldichlorosilane, phenyl beta cyanoethyldichlorosilane, phenylgamma cyanopropyldichlorosilane, cyanohexyl-beta-cyanopropyldichlorosilane. The cyanoalkyldiorganochlorosilanes of formula (2) are characterized by the fact that the nitrile group is attached to a carbon atom which is at least one carbon atom removed from the silicon atom. For example, the cyano group is beta or gamma with respect to the silicon atom. Silanes which come within the scope of formula (3) are as follows: trimethylchlorosilane, dimethylphenylchlorosilane, dimethyl-beta-cyanoethylchlorosilane, and diphenyl-gamma-cyanopropylchlorosilane.

To form the ester alkylpolysiloxanes of formulas (5) and (6) the diorgano hydrolyzable silane of formula (1), the cyanoalkyl hydrolyzable silane of formula (2) and the silane of formula (3) are mixed together in the proportion that the siloxy groups appear in the ester alkylpolysiloxane. This mixture is then slowly added to water to facilitate the hydrolysis and condensation of the siliconbonded halogen hydrolyzable atoms and the hydrolysis of the nitrile groups to carboxyl groups. In general, the amount of water employed in the hydrolysis and condensation reaction is sufiicient to hydrolyze all the siliconbonded hydrolyzable atoms and also sufficient to provide a solvent for the acid which may result from the hydrolysis, which may be hydrogen chloride assuming that the hydrolyzable radical is chlorine. Preferably, the amount of water is maintained at a value sufiiciently low to provide a concentrated hydrogen chloride solution or other acid solution or even so low as to be insufiicient to dissolve all of the acid formed. Where the amount of water is insufficient to dissolve the acid generated, it is desirable to maintain the reaction mixture under pressure, such as a pressure of about 50 lbs/in. so as to avoid loss of the acid. In general, the amount of water employed is from about 0.75 to about 1.25 parts per Weight of the mixture of the three hydrolyzable silanes of formulas (1), (2) and (3). The hydrolysis and condensation reaction is found to be exothermic and it is found that the temperature increases to within a range of 25 to C. and preferably to a maximum in the range of about 70 C. during the course of the hydrolysis and condensation, which is effected in the period of time of about generally 1 to 8 hours and preferably 1 to 6 hours. After completion of the hydrolysis and condensation reaction, water and acid are stripped to yield a reaction mixture containing the precipitate of ammonium halogen from the hydrolysis of the nitrile group to the carboxy group. This precipitate is filtered and the reaction mixture is then dried. In order to insure a uniform composition, the dried and filtered hydrolyzate is equilibrated with sulfuric acid. The conditions under which this equilibration is eifected can vary Within extremely wide limits. In general, satisfactory results are obtained by adding from about 1 to 5% by Weight of 86% sulfuric acid to the hydrolyzate and heating the reaction mixture at a temperature of from about 70 to C. for a period of time from about 1 to 6 hours, and preferably 1 to 3 hours. At the end of this time, the reaction mixture is cooled and washed with water until the wash water is neutral. This results in the carboxyalkylpolysiloxane of formula 4. I

The carboxyalkylpolysiloxane of formula 4 may also be obtained by an alternate procedure. Assuming the hydrolyzable radical in formulas (1), (2) and (3) is chlorine, such polysiloxanes can be produced by following the procedure involving the hydrolysis of one or more of the above hydrocarbon-substituted chlorosilanes, in which the substituents consist of saturated hydrocarbon groups which compounds of formulas (l) and (2) and (3) are first hydrolyzed separately. The silane of formula (3), when hydrolyzed, will produce a disiloxane which can be separated by distilling off the other constituents in the reaction mixture and the volatiles. The silanes of formulas (1) and (2) are hydrolyzed separately to produce a mixture of linear and cyclic polysiloxanes. The two crude hydrolyzates are then polymerized by treatment with KOH and being heated at elevated temperatures to form a mixture of low boiling, low molecular weight cyclic polymers, having the formulas,

where c and d are whole numbers varying from 3 to 10. The crude hydrolyzate containing the above cyclics also contain undesirable materials such as monofunctional and trifunctional chlorosilane starting material. The bydrolyzates of cyclic and linear siloxanes are fractionally distilled and there is collected two pure products containing low boiling, low molecular weight cyclic polymers free of any significant amount of monofunctional and trifunctional groups.

Because of the nitrile group, when the hydrolyzate of the chlorosilane of formula (2) is hydrolyzed, it is preferred that a strong acid be utilized as the catalyst. Examples of such strong acids useful as catalysts in the depolymerization reaction are sulfuric acid and toluene sulfonic acid. Thus, after the two hydrolyzates are contacted with a strong acid and heated to a temperature above 150 C. for a period of 1 to hours and preferably 4 to 8 hours, the reaction mixture can be distilled to produce a distillate consisting essentially of low molecular weight cyclic diorgano polymers free of any significant amounts of monofunctional and trifunctional groups. These cyclic siloxanes which are prepared in accordance with the above procedure and which are represented by formulas 7 and 8 are added in the desired proportions in the reaction vessel so as to be subjected to an equilibration reaction to form the carboxyalkylpolysiloxane of formula 4. To this mixture of the cyclic polysiloxanes of formulas 7 and 8 there is added in a desired proportion a disiloxane of the formula,

in the correct proportions so that the disiloxane can function as a chain-stopper to limit the chain length of the polysiloxanes formed. The reaction mixture can then be equilibrated to form the carboxyalkylpolysiloxane of formula 4.

In order to carry out the equilibration reaction, there must be added to the reaction mixture a catalyst which is selected from a strong base or a strong acid such as potassium hydroxide, sodium hydroxide, sulfuric acid, toluene sulfonic acid and other acids. It is preferred to use a strong acid, such as toluene sulfonic acid, as the catalyst in order to preserve the carboxy group in the polysiloxane product. Functional compounds that may be employed satisfactorily for controlling polymer growth withinthe scope of the disiloxane of formula 9' include among other hexamethyldisiloxane, tetramethyldiethoxydisiloxane, diethyltetraethoxydisiloxane, and divinyltetra- 'ethoxydisiloxane. The equilibration reaction is carried out from 2 to 4 hours until about 85% of the cyclic diorganosiloxanes have been converted to polymers end-stopped with monofunctional groups. When the 85% conversion point has been reached, there are just as many polymers being convertedto cyclic siloxanes as there are cyclic siloxanes being converted to the polymer. At that time there is added to the mixture a suflicient amount of an acid donor or a base such as ammonium hydroxide that will neutralize the toluene sulfonic acid so as to terminate the polymerization reaction. The cyclic diorganosiloxane reactants that are left are then distilled off to leave the 8 carboxyalkylpolysiloxane fluid which is useful in the present invention.

The above procedure has been described for the case where R is preferably methyl. However, the above procedure will apply in the case where R is represented by groups other than methyl, such as ethyl, vinyl, etc. More specifically, with respect to the case where R is methyl, g is equal to 2 in formulas 1), (2) and (3). Preferably carboxymethylpolysiloxane can be produced by equilibrating hexamethyl disiloxane with octamethyltetrasiloxane and tetramethyltetra-beta-cyanoethyltetrasiloxane in the proper molar proportions in the presence of '3 of acid treated clay, such as fullers earth and the reaction mixture is heated for 5 hours at to C. to equilibrate the reaction mixture. After 5 hours of reaction time, when approximately 85% of the tetramers have been converted to the polymer polysiloxanes, the catalyst is neutralized with a weak base and the volatile cyclics are distilled off to leave a substantially pure carboxyalkylpolysiloxane. By using beta-cyanoethyltetramethyldisiloxane as the chain-stopping unit instead of hexamethyldisiloxane, there can be obtained a linear polysiloxane having acid groups at terminal positions of the polymer chain, as well as the center position of the polymer chain. Such a polymer product permits esterification with an alcohol so that the alcohol groups are attached to terminal positions of the polymer chain, as well as to positions within the center of the polymer chain. The carboxyalkylpolysiloxane of formula 4 may then be esterified with an alcohol selected from the group of R OH, R OR OH,

ll PJC-O Ii -OH,

R g-B UE, HO-R OH and HO-R (OH) where R R R and s are as defined above. The preferable alcohol for esterification is methanol or CH OCH CH OH. The alcohol is added to the carboxyalkylpolysiloxane in the presence of a good esterification catalyst. Although an esterification catalyst is not needed, thereaction proceeds too slowly without such a catalyst. Examples of good esterification catalysts are strong acids, such as sulfuric acid, hydrochloric acid or nitric acid. Preferably, the catalyst is sulfurie acid or toluene sulfonic acid. Further, although the' reaction may be carried out at room temperature, it has been discovered that the esterification reaction proceeds too slowly at that temperature. Preferably, the reaction temperature is in the range of 70 to 150 C. and more preferably in the range of 70 to C. The acid catalyst is added to the reaction mixture at a concentration of 1 to 10% by weight and preferably 1 to 5% by weight, of the esterification reactants. Further, although the esterification may be carried out without a solvent, it is preferred to add a solvent to the reactants so as to azeotrope out the water of esterification that is formed while the esterification proceeds to completion. Such a solvent may be selected from xylene, toluene, benzene and mineral spirits. Into the reaction vessel there is added the solvent, then there is added the carboxyalkylpolysiloxane and the catalyst. The reaction mixture is then heated above 50 C. and preferably 70 to 130 C. and at this time there is slowly added the alcohol to the reaction mixture. All of the alcohol is not added immediately but is added slowly during the course of the reaction. Preferably, one-half of the alcohol or one-third of the alcohol is added immediately at the beginning of the reaction and then the rest of the alcohol is added at'subsequent points in the esterification reaction. The water that; is formed in the esterification reaction is continually azeotroped with the solvent out of the reaction mixture so as to allow the esterification reaction to proceed to completion. Preferably, the esterification reaction takes from 1 to 10 hours and preferably from 5 to 10 hours. Thus, to allow the re' action to proceed with the continual removal of the water that is formed in the esterification reaction, it is desirable to add one-half of the alcohol to the reaction mixture at the beginning of the reaction and then after 2 or 3 hours have passed to add the rest of the alcohol to the reaction mixture. Conversely, the alcohol can be slowly and continuously added to the reaction pot in over a period of 3 to 7 hours from the initial beginning of the reaction. Preferably, the carboxyalky-lpolysiloxane and the alcohol are reacted in stoichiometric amounts. However, it is not unusual and, in fact, it is desirable to add some alcohol in excess to the stoichiometric amount that is necessary to react with the carboxy groups in the polysiloxane. The excess amount of alcohol insures that the esterification of the carboxyalkylpolysiloxane will go to completion. In addition, it is most desirable to add at least 10% in excess of alcohol in the case where the alcohol is a polyol, that is, a dihydroxy alcohol or a dihydroxy, trihydroxy, etc., type of alcohol. The excess alcohol is desirable in these cases where there is a polyol in order to prevent the formation of diesters. After the esterification reaction has proceeded to completion, that is after the preferable reaction time of to hours, the acid is neutralized with sodium bicarbonate. After the neutralization with the sodium bicarbonate, the solvent and the lower boiling siloxanes which are formed can be stripped off by boiling the reaction mixture at a temperature above 200 C. and at atmospheric pressure or reduced pressure. The fiuid remaining after this stripping step is the desired ester polysiloxane product of formulas (5) and (6).

It has been mentioned previously that the diorganosilane of formula 1) and the silane of formula (3) are standard materials well known in the prior art. In fact, the cyanoalkylsilane of formula (2) is also a well known standard material of the prior art. However, the process for producing it is somewhat involved. One method of producing the nitrile silane of formula (2) and, of course, the nitrile silane of formula (3), where there is a nitrile group attached thereto, is to react an olefinic cyanide with the alkylhydrochlorosilane in the presence of a three component catalyst system disclosed in Bluestein U.S.P. 2,971,970. This is an SiI-I-olefin addition reaction that is used to obtain the product. For instance, allyl cyanide may be reacted with methyldichlorosilane to obtain methyl-gamma-cyanopropyldichlorosilane. The reaction proceeds in the presence of a three-catalyst system which comprises a cuprous compound selected from the class consisting of cuprous halides and cuprous oxides, a diamine having the formula where m is an integer from 1 to 6, inclusive, R is a lower alkyl radical and R is a member selected from the class consisting of hydrogen, lower alkyl radicals, aminoalkyl radicals, alkyl-amino radicals and dialkylaminoalkyl radicals and mixtures thereof. In the preferred utilization of the catalyst, the catalyst system also includes a trialkylamine in addition to the cuprous compound and diamine previously mentioned, which trialkylamine is represented by the formula (Y) n Where Y is an alkyl radical.

In addition to the difunctional betacyanoalkylsilanes that can be produced by this catalyst system, it is also useful in the preparation of trifunctional and monofunctional beta-cyanoalkylsilanes, such as betacyanoethyltrichlorosilane, by the addition of trichlorosilane to acrylonitrile and beta-cyanoethylmethylchlorosilane b addition of methylchlorosilane to acrylonitrile. Utilizing this three or two-component catalyst system, a hydrolyzable silicon hydride is reacted with a beta-unsaturated olefinic nitrile where the hydrolyzable silicon hydride is described by the following formula:

formula:

where Y represents the same or different members selected from the class consisting of hydrogen and lower alkyl radicals, e.g., alkyl radicals having from 1 to 8 carbon atoms. Among the specific nitriles within the scope of the above formula may be mentioned, for example, acrylonitrile, methacrylonitrile, ethylacrylonitrile, l cyanobutene-l, 2 cyanooctene 1, etc. The addition of the hydrolyzable silicon hydride within the scope of formula (1) to the alpha-beta-unsaturated olefinic nitrile results in the formation of a hydrolyzable beta-cyanoalkylsilane within the scope of formula (2).

As previously mentioned, one of the components of the multiple component catalyst system of the present process set forth is a diamine within the scope of formula 10. Specific diamines within the scope of formula 10 include, for example, N,N,N tetramethylethylenediamine, N,N,N tetraethylethylene diamine, etc. Another component of the catalyst system may be trialkylamine, which can include, for example, trirnethylamine, triethylamine, tributylamine, triamylamine, trioctylamine, methyldiethylamine, dimethylbutylamine, methylbutyloctylamine, dimethyl-octa-decylamine, etc. In carrying out the reaction, the olefinic nitrile, the silicon hydride and the catalyst system are merely added to a suitable reaction vessel and maintained at a desired temperature for sufficient time to effect the reaction. The time required for effecting the reaction varies greatly, depending upon the particular reactant, the particular catalyst system employed and the temperature of the reaction. Of the various olefinic nitriles employed in the practice of this process, the fastest reaction rate is observed with acrylonitrile. As the acrylonitrile becomes more substituted, the reaction rate decreases. The reaction rate is also a function of Whether the two-component catalyst system or the three-component catalyst system is employed. Reactions involving the three-component system of the diamine, the trialkylamine and the cuprous compound are generally faster than the reactions involved with the catalyst system which does not contain the trialkylamine. The reaction rate is also a function of the particular diamine employed, in either the two-component catalyst system or the threecomponent catalyst system. It has been discovered that the compound N,N,N',N' tetramethylethylenediamine is by far the most efiicient of the diamines and produces the most rapid reaction under the least vigorous reaction conditions for the best yields of the desired addition product. As the methyl groups are replaced with the hydrogen or alkyl radicals higher than methyl, the reaction rate begins to fall so that higher temperatures or higher catalyst concentration or longer reaction times are required to produce equivalent results. As mentioned previously, the multiple component catalyst composition can contain either two-components or three components, and except as noted, no critical catalyst component concentration has been found. The catalyst composition may be described broadly as being selected from the class consisting of (a) a first mixture of a diamine, a trialkylamine, and a cuprous compound selected from the class consisting of cuprous halides and cuprous oxides, and (b) a second mixture of a diamine and a cuprous compound selected from the class consisting of cuprous halide and cuprous oxide, the total number of atoms of nitrogen in each of said mixture being in excess of the total number of copper atoms in each of said mixtures. The requirement that the number of atoms of nitrogen be in excess of the number of atoms of copper in the catalyst mixture is a critical feature. In tlie'preferred embodiment of the process, the catalyst composition comprises in a mole ratio basis, from 0.1 to 20 moles'of diamine within the scope of formula 10, from to 20 moles of trialkylamine and from 0.1 to 20 moles of a cuprous compound, again with the total number of nitrogen atoms being in excess of the number of moles of copper atoms.

In general, there should be at least about excess of nitrogen atoms over copper atoms. Where all three components are present in the reaction mixture, the preferred composition on a mole ratio basis is from 0.1 to moles each of the diamine, the trialkylamine and the cuprous compound. The amount of catalyst composition employed in relation to the monohydrolyzable silicon hydride and the olefinic nitrile may again vary within extremely wide limits. As is the case with most catalytic reactions, the rate of reaction increases as the catalyst concentration increases, and although no critical catalyst concentrations have been discovered, for economic reasons it is preferred to employ, on the basis of total moles of hydrolyzable silicon hydride and olefinic nitrile, at least 0.1 mole percent of the diamine and at least 0.1 mole percent of the cuprous compound. The ratio of the hydrolyzable silicon hydride to the alpha-beta-unsaturated olefinic nitrile may be varied within extremely wide limits. However, since the addition reaction involves 1 mole of the hydrolyzable silicon hydride for 1 mole of the alphabeta-unsaturated olefinic nitrile, in the preferred embodiment of the process, equimolar amounts of reactants have been employed. The use of molar excesses of either of the two reactants is not precluded. Reactions have been elfected with ten-fold molar excesses of either reactant. However, no particular advantage is derived from the excess of either reactant and, in fact, the economics of the reaction make it preferable to employ substantially equimolar amounts.

In carrying out the process, the hydrolyzable silicon hydride, the alpha-beta-unsaturated olefinic nitrile and the three components of the multiple component catalyst system are added to the reaction vessel in any order. There are no adverse effects by varying the order of addition of the reactants. In general, it is desirable to agitate the reaction mixture to obtain optimum reaction rates. However, agitation is not critical to the successful completion of the reaction. One of the most useful methods of agitating the reaction mixture is by heating the reaction mixture at a reflux temperature after the reaction is completed. General refluxing of the reaction mixture provides suitable agitation and optimum reaction rates.

Generally, the temperature of the reaction mixture varies during the course of the reaction and varies also depending on the particular reactants. Generally, however, the reflux temperature of the reaction is from about 50 C. to about 130 C. In addition to refluxing the reaction mixture under atmospheric conditions, the reaction mixture may be heated at reflux temperature corresponding to reduced pressures or elevated pressures. At higher pressures, the reflux temperatures will increase correspondingly, for example, to a temperature of 120 to 150 C. While increasing the pressure, the reflux temperature under which the reaction is conducted increases the reaction rate somewhat, it has been found that the most convenient means of effecting the reaction is at atmospheric pressure in conventional equipment rather than in the pressure equipment required for higher pressure operation. It should also be understood that the reaction of the present invention may be effected by placing the reactants in the pressure vessel and heating the contents of the vessel at an elevated temperature. In addition to'conducting: the reaction at the reflux temperature, the reaction will also proceed at temperatures as low as room temperature with or without agitation. The reaction may also be carried out in the presence or absence of inert solvents. Preferably, no inert solvent is used in the reaction. However, the use of solvents which are inert under the reaction conditions are not precluded. Such solvents include, for exampleace'to; nitrile. Thus, the above process may be carried out to produce difunctional beta-cyanoalkylsilanes such as that of formula (2). However, this process, while it can be used to produce the difunctional beta-cyanoalkyl'silanes of formula (2), it can also be used to produce monofunctional beta-cyanoalkylsilanes such as that of formula (3). Thus, by using this process, the cyanoalkylsilanes of formula (2) and formula (3) may be prepared so that in accordance with one embodiment of the present invention these cyanoalkylsilanes may be hydrolyzed with the diorganosilane of formula (1) to produce the carboxyalkylpolysiloxane of formula 4. v

The ester polysiloxane products of formulas (5) and (6) meet the requirements and criteria which have been set forth above,

The present invention sets an alternate process by which the same ester polysiloxane brake fluids as that claimed in the above-mentioned Travers application can'be prepared. The basic advantage of the process of the present invention from that set forth in the Travers Ser. No. 125,398 is that there is no need for an alkenoic acid as a starting material in the process. In the present process, all the starting materials are common chemical materials of which there are large quantities in the market. Also in accordance with the present process, it is not necessary for platinum catalyst to be used, sincethe cyanoalkylsilanes may be prepared by a process in which no platinum catalyst is used, as set forth above. f

The following examples are set forth below for the purpose of illustrating the invention andare not intended to limit the invention in any way or form. All parts are by weight unless specified otherwise.

Example 1 Into a 5 liter, 3neck round bottom flask which was equipped with a mechanical stirrer, Y-head, thermometer addition funnel, condenser and heating mantle was added 1687 parts of octamethyltetracyclicsiloxane, 396 parts of tetramethyltetracyanoethyltetracyclicsiloxane, and 918 parts of cyanopropyltetramethyldisiloxane. After the three reactants had been mixed and the temperature raisedto 70 C., there was added parts of toluene sulfonic acid and the reaction mixture was heated to to C. for 8 hours with continual reflux taking place. At the end of this reaction period, there was added to the reaction mixture 45 parts of sodium bicarbonate and acetone to neutralize the catalyst, that is, the toluene sulfonic acid. The low boiling siloxanes, as well as the cyclic siloxanes', were then stripped off the solution at a stripping temperature of 200 and at 1.5 mm. pressure. The liquid remaining in the reaction flask was carboxyalkylpolysiloxane having the formula:

[CHaSiOlSflCHsh uomnooon (CH:)2C00H Example 2 Into a 5 liter, 3-neck round bottom flask equipped with a mechanical stirrer, a Y-head, a thermometer, addition funnel, condenser and heating mantle there was added 2000 parts of the carboxyalkylpolysiloxane product of Example 1. To this carboxyalkylpolysiloxane was added 40 parts of toluene sulfonic acid. The mixture was equilibrated for 3 hours at 110 C. At the conclusion of 3 hours equilibration period 300 parts of methanol, and 20 parts of toluene sulfonic acid wereadded at 80 C. and held there for A1 hour before adding 1,000 cc. toluene solvent to azeotrope out water formed by the esterific'ation. The process of adding methanol, and azeotroping out methanol and water is repeated twice more using 300 parts methanol each for 3 hour cooking periods prior to initiation of each azeotrope. The reaction pot temperature is controlled between 80 and 120 C. At the conclusion of the esterification which was'followed on infrared analysis the strong acid was neutralized with sodium bicarbonate. The solvent and lower boiling siloxanes was stripped out at 200 C. at 1.5 mm. pressure. The fluid remaining in the reaction flask is then colorized with carbon black, fullers earth and then filtered through Celite 545 to yield a water-white liquid having the structure The viscosity properties of this ester polysiloxane product is as follows:

Temperature: Viscosity and centistokes -67- F. Approximately 600. 77 F. u "Approximately 17. 100 F. Approximately 13. 210 F. Approximately 5.

and then 0.25 mm. increments to a water level. The pot is reheated until boiling temperature is recorded then the pot is cooled to less than 250 F, before the next increment of water is added and the cycle repeated. By using this procedure, the following boiling points were obtained for the methyl ester polysiloxane whose structural formula is given above in conjunction with different amounts of water being incorporated as follows:

Temperature! 1 Percent water 710 F. 600 F. 0.1

' 530 F. 0.2 470 F. 0.3 430 F. 0.4 390 F. T 0.5 300 F. 1

Example 3 To 2000 parts of the carboxyalkylpolysiloxane of Example 1 there is added 60 parts of toluene sulfonic acid. The fluid is equilibrated for 3 hours at 110 C. and at the conclusion of the 3 hour equilibration, 500 parts of methoxyethanol and 20 partsof toluene sulfonic acid were added at 90 C. for 20 minutes before adding 1,000 cc. of toluene to azeotrope out water formed by the esterification. The process of adding methoxyethanol and azeotroping off methoxyethanol and water was repeated twice more using 500 parts of methoxyethanol each and 3 hour cooking periods prior to initiation of the azeotrope after each cooking period. Pot temperature was maintained at 90 to 110 C. At the conclusion of the esterification which was followed by infrared analysis, the strong acid was neutralized with N HCO The solvent and lower boiling siloxanes were stripped out at 200 C. and 1.5 mm. pressure. The fluid was filtered through carbon black and fullers earth and then Celite 545 to yield a water-white liquid having the following structure;

Into a 5 liter, 3-neck round bottom flask equipped with a mechanical stirrer, Y-head, thermometer, addition funnel, condenser and heating mantle there was added 2,000 parts of to the above carboxyalkylpolysiloxane there was added 50 parts of toluene sulfonic acid. The fluids are equilibrated for 2 hours at 120 C. At the conclusion of the two hour equilibration, 900 parts of and 40 parts of toluene sulphonic acid was added at C. and held for 1 hour before adding 1000 cc. toluene to azeotrope water formed by the esterification. The process of adding alcohol and azeotroping ofl alcohol and water is repeated twice more using 300 parts of the alcohol each time and a low pour azeotype period prior to the initiation of the azeotrope. The reaction pot temperature is maintained at -120 C. At the conclusion of the esterification the strong acid is neutralized with N HCO and the solvent and the lower boiling siloxanes are stripped out at 190 C. and at 1.5 mm. pressure. The fluid that remains in the reaction pot decolorized with carbon black and fullers earth and then filtered through Celite 545 to yield a compound of true structure,

(CHQ SiO[(CHQzSiOlalCHzSiOhSi(CH1): 0

wmnooowmn-oom Example 5 Into a 5 liter, 3-neck round bottom flask equipped with a mechanical stirrer, Y-head, thermometer, addition funnel, condenser and heating mantle is added 1500 parts of a carboxyalkylpolysiloxane of the formula,

and 60 parts of toluene sulfonic acid. The fluid is equilibrated for 4 hours at 110 to C. At the conclusion of the 4 hours equilibration period, there is added 1100 parts of HO(CH -OH, 40 parts of toluene sulfonic acid and the reaction mixture is heated to 90 C. and held there for 1 hour before adding 1,000 cc. toluene to azeotrope out water formed by the esterification. The process of adding the diol and the azeotroping of the diol and water is repeated twice more using 300 parts of the diol each and a 4 hour cooking period prior to initiation of the azeotrope. The reaction pot temperature is controlled between 90 and C. At the conclusion of esteriflcation which is followed by infrared analysis, the strong acid neutralized with a solution of sodium bicarbonate and acetone. The lower boiling siloxanes and solvent are stripped of it at C. at a pressure of 1.5 mm. of mercury. The fluid is decolorized with carbon black and fullers earth and then filtered through Celite 545 to yield a water-white liquid of the structure,

( QQ K ah holo z h 2):

( 2)10CO O (CH2) 0H This fluid which is useful as a brake fluid has 'a viscosity at 40 F. of 2400 centistokes.

What I claim as new is:

1. A process for forming an ester polysiloxane useful as a brake fluid comprising (a) hydrolyzing in a first reaction in the presence of water a diorganosilane of the formula,

R siX with a cyanoalkylsilane of the formula,

RSi(X )C H CN and a silane of the formula,

R'R SiX where R is selected from monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals,

15 R is selected from the class consisting of R and C H CN, X is a hydrolyzable radical selected from halogen, alkoxy, aryloxy and acyloxy radicals, g is a whole number that varies from 1 to 20, (b) equilibrating the resulting mixture in the presence of 1 to 5 percent of H 80, by weight of the polysiloxane in the reaction mixture at a temperature in the range of 75125 C. for 1 to 5 hours, to obtain polysiloxane of the formula,

and (c) then esterifying the above product in the presence of a catalyst which is toluene sulfonic acid with an alcohol selected from the group consisting of ROH, R OR H,

II I; R C-R 011, R -0-R -0H OHR -OH and OHR (OH) where y varies from 1 to 10, z varies from 1 to 15, R is selected from monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, R is a polyvalent hydrocarbon radical with s-+1 hydroxyl groups attached thereto, s is a whole number that varies from 1 t0 5 and R is a divalent hydrocarbon radical selected from alkylene and arylene radicals of less than 20 carbon atoms.

2. The process of claim 1 wherein said first reaction is carried out at a temperature in the range of 25- 100" C.

3. The process of claim 1 wherein there is used 075 to 1.25% by weight of water based on the weight of the reaction mixture in said first reaction.

4. The process of claim 1 wherein said first reaction is carried out for 1 to 8 hours.

5. The process of claim 1 wherein R is methyl, g is equal to 3, and R is methyl.

6. The process of claim 1 wherein the esterification reaction is carried out at a temperature in the range of 70 to 150 C. in a period of 1 to 10 hours.

7. A process for forming an ester polysiloxane useful as a brake fluid comprising (a) reacting in an equilibration reaction and in the presence of acid treated clay a cyclopolysiloxane of the formula,

so as to equilibrate the reactants where R is methyl, R

is selected from the class consisting of R and C H- CN ,16 g is 2, a and b are whole numbers that vary' froni -la to 10, to obtain a polysiloxane of the formula, i

R 3,310 (R510) (RgSi0) .simu' j ,nacoon H (b) separating the above product, and (c) then esterify ing the said product by reacting it in the presence of a catalyst which is toluene sulfonic acid at a temperature of to 150 C. with an alcohol selected from the group consisting of R OH, R 0R OH,

m-O-JBOH, R -R 011 .1' i OHR OH and OHR (OH) where y varies from 1 to 10, z varies from 1'10 15, R is selected from monovalent hydrocarbon radicals and halogenated monovalent hydrocarbon radicals, R is a polyvalent hydrocarbon radical with s+1 hydroxyl groups attached theretoand s is a whole number thatvaries from 1 to 5 and R3 is a divalent hydrocarbon radical selected from al kylene and arylene radicals of up to 20 carbon atoms, f

8. The process of claim 7 wherein the equilibration reaction is carried out at a temperature of -120 C. for up to 5 hours. 9. The process of claim 7 wherein R is methyl. 10. The process of claim 7 wherein R is 11. The process of claim 7 further comprising adding NaHCO to the reaction mixture after the esterification reaction is completed, stripping off low boiling polysiloxanes at a temperature in the range of -250 C. at reduced pressure and filtering out the precipitate that" is formed from the reaction product to yield the pure ester JAMES O. THOMAS, IR., Primary Examiner" *1 D. G. RIVERS, Assistant Examiner r Us. 01. X.R. v 

